1. Field of the Invention
The present invention relates to a galvanometer controller for controlling a galvanometer which performs scanning with a laser beam at high speed and with high accuracy, and to a laser machining apparatus having the galvanometer controller.
2. Description of the Prior Art
Laser machining apparatuses have been used to perform boring, cutting, welding, marking, trimming, etc., on workpieces. Also, for machining, methods of scanning a laser beam on a workpiece in two-dimension are generally used. In one method, the laser beam is scanned by using a galvanometer or a polygon mirror, and in the other method, scanning is alternatively performed by moving an X-Y table on which a workpiece is mounted.
The X-Y table scanning method has problem of difficulty in performing high-speed driving, problem of slow response, and problem of the overall size of an apparatus being increased. In contrast, the galvanometer scanning method using a galvanometer which performs rotational drive along each of X- and Y-directions has the advantages of enabling high-speed scanning, ensuring high accuracy, and enabling an apparatus including the scanner to be simplified in construction and reduced in size.
A laser machining apparatus using a galvanometer performs machining in such a manner that rotational operations of the galvanometer having two axes along X- and Y-directions are controlled by a rotational drive unit, and a workpiece is irradiated with a beam of laser light reflected by mirrors and condensed by an optical unit such as a condenser lens and is worked by being molten and evaporated by the energy of the laser beam, as shown in FIG. 1 This type of laser machining apparatus has a high resolution on the order of microradians and a wide scanning angle, is capable of high-speed operation, and is particularly suitable for use in the field of working for accurately forming fine holes of a size on the order of microns.
The galvanometer in the laser machining apparatus has a position sensor such as a capacitance sensor for detecting the position of each the mirror. The galvanometer is accurately driven at a high speed by feedback control using a sensed position signal from the capacitance sensor.
However, the conventional controller for controlling the galvanometer used to perform scanning with a laser beam in laser machining apparatuses is conventionally constituted by analog circuitry elements and therefore has problems described below.
First, during use of the galvanometer after the time when the galvanometer is initially adjusted, the adjusted state is changed due to changes with time in analog devices constituting the analog circuit. That is, generally speaking, devices constituting a circuit change with time, and changes with time in the devices are inherently added on a processed signal. For this reason, an error occurs in galvanometer position control.
Second, a change in the adjusted state of the galvanometer is caused by characteristic changes of analog devices constituting the circuit according to environment temperature change. That is, in a case where temperature of an environment in which the laser machining apparatus is installed may vary largely, a considerable change occurs in the characteristic of the control circuit and therefore frequent galvanometer position adjustment is inherently required according to changes in environment temperature.
Third, in general, an analog circuit has many adjustment points such as variable resistor adjustments and an increased number of process steps and, therefore, a skilled person for fine adjustments is also required. Accordingly, in the adjustment based on the usage of the analog circuit, a complicated adjustment procedure is required and it becomes difficult for persons other than those experienced in handling the apparatus to perform adjustment operations.
Fourth, it is difficult to quantitatively grasp the adjusted state of the galvanometer because the galvanometer is adjusted through setting of variable analog circuitry elements, and the desired control quality cannot be obtained with stability. That is, in the analog adjustment, experience and intuition which a skilled operator has are important factors, and the adjustment varies with operators, so that the apparatus cannot always be operated in the same condition.
Fifth, in a case where a new function is required to the galvanometer controller, the controller hardware itself must be changed since the controller is constituted by the analog circuit. Accordingly, it is difficult to expand or add functions in the controller using the analog circuit elements.
Sixth, in general, characteristics of a galvanometer varies according to temperature change and humidity change. Thus, even if a circuitry characteristic of a galvanometer controller is kept constant under the condition of temperature change, characteristics of a galvanometer itself inherently varies according to the temperature change and humidity change, thereby causing erroneous operation.
In view of the above-described problems, an object of the present invention is to provide a galvanometer controller capable of controlling a galvanometer with stability and with immunity to changes with time and variation in environment temperature and having improved operability and expandability.
Another object of the present invention is to provide a laser machining apparatus having the galvanometer controller mentioned above.
To achieve the above-described object, according to the present invention, there is provided a galvanometer controller which controls the direction of laser scanning performed by a galvanometer on each of two axes, the galvanometer controller comprising a correcting arrangement formed in a digital circuit, further, the correcting arrangement having a distortion correction section for correcting a working distortion of an optical unit including a lens, an orthogonality correction section for correcting the orthogonality between the two axes of the galvanometer, and a linearity correction section for correcting the linearity on each of the two axes. Further, it is preferred that the galvanometer controller includes a temperature/humidity detector and characteristic controlling means for controlling a characteristic thereof according to the temperature change or humidity change.